The invention relates to a generator such as is often used, for example, on a turbine engine. In particular, but not exclusively, the invention relates to a starter/generator suitable for use in initiating start-up of a turbine engine.
It is well known to use both AC and DC generators as starters for motors and engines. For example, generators are commonly used as engine starters on small aircraft engines, such as gas turbine engines, using either battery or ground-source power. The generator armature is supplied with electrical current and the generator develops substantial torque to begin turning of the engine. After the engine has been started, the generator is typically used as an electrical power source for the aircraft.
The starter/generator includes a power drive shaft having a drive end spline which is adapted to be coupled to an engine drive shaft, in use, to effect engine start-up. It has been recognised that, in the event of a system fault, the potential exists for electrical leakage current to flow through the power drive shaft to the engine drive shaft. Such current leakage is undesirable and one proposed means for avoiding this problem is to provide an insulator arrangement on the engine drive shaft within the associated engine gearbox. A disadvantage of this, however, is that the accommodation space available for an additional insulating arrangement within the engine gearbox is limited. It is also difficult to modify existing engines to include this component.
It is an object of the present invention to provide a generator suitable for use as a starter/generator on a gas turbine engine which alleviates or removes the aforementioned problems.
According to the present invention, there is provided a generator comprising a generator housing, a generator drive shaft including a power input shaft coupled to a drive member through a coupling arrangement, whereby in use the drive member is coupled to an output shaft of an associated engine, the coupling arrangement being arranged within the generator housing and comprising first and second coupling members and an insulator member interposed between the first and second coupling members and arranged such that the input shaft is electrically insulated from the drive member, and hence from the engine output shaft, in use.
In a preferred embodiment, the generator takes the form of a starter/generator for use on a turbine engine, having a starter or start up mode of operation in which drive is transmitted from the power input shaft to the drive member and, hence, to the engine, and a generator mode of operation in which drive is transmitted from the drive member to the input shaft. It will be appreciated, however, that the generator may be used in other applications, in which electrical insulation of the generator drive shaft and the driven output shaft is desirable.
As the starter/generator is provided with an electrically insulating member between the first and second coupling members, through which drive is transmitted from the power input shaft of the generator drive shaft to the drive member associated with the engine output shaft during the start up mode of operation and through which drive is transmitted from the drive member to the input shaft during the generator mode of operation, the risk of electrical current leakage from the generator drive shaft to the output shaft of the associated engine is substantially avoided. Furthermore, as the insulator member is arranged inside the generator housing, the need for an external insulator arrangement within the engine gearbox can be avoided. The insulator member can also be retrofitted to existing generators with relatively little modification of existing generator parts.
Preferably, the generator takes the form of a DC generator, but it may alternatively take the form of an AC generator.
Preferably, the drive member includes a spline arrangement through which the drive member is coupled to the output shaft of the associated engine, and hence, by virtue of the coupling arrangement, by which the power input shaft is coupled to the engine output shaft. The second coupling member may form an integral part of the drive member, or alternatively may be a separate component carried by the drive member. For example, the drive member may take the form of a separate adapter member carried by the drive member.
The coupling arrangement preferably includes securing means for securing the first and second coupling members and the insulator member together. The securing means may include one or more securing element.
Preferably, each of the first and second coupling members and the insulator member is provided with an aperture or drilling within which a securing element is received, at least in part.
In one embodiment of the invention, the insulator member is provided with first and second apertures or drillings, a first securing element being received within the first aperture and a corresponding aperture or drilling provided in the first coupling member, a second securing element being received within the second aperture provided in the insulator member and a further corresponding aperture or drilling provided in the second coupling member. The first and second apertures provided in the insulator member are arranged such that, when the first and second securing elements are received within their respective apertures, the first and second securing elements are electrically insulated from one another.
In an alternative embodiment of the invention, the securing means includes a single securing element which extends, at least in part, through respective apertures or drillings provided in the first and second coupling members and within the insulator member.
In this embodiment, the coupling arrangement preferably further comprises further insulator means for electrically insulating the securing element from the first and second coupling members.
The further insulating means may comprise an insulating sleeve received, at least in part, within the apertures provided in the first and second coupling members and in the insulator member.
The first coupling member may take the form of a first damper plate forming part of a damping arrangement which serves to prevent transmission of vibrations within the generator to the engine shaft.
The coupling arrangement may further comprise a second damper plate and a friction ring arranged between the first and second damper plates.
Preferably, one or more of the securing elements takes the form of a bolt.